Disc drives are common data storage devices. A typical disc drive includes a rigid housing or deck that encloses a variety of disc drive components. The components include one or more discs having data surfaces coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor that causes the discs to spin and the data surfaces of the discs to pass under respective hydrodynamic or aerodynamic bearing disc head sliders. The sliders carry transducers, which write information to and read information from the data surfaces of the discs.
A flexible circuit, known as a “flex cable” and typically including electrical traces supported by a polymeric carrier material connects the read\write elements on the disc head slider to the arm electronics, which interface the data signal from a host computer with the disc.
A head stack assembly (HSA) in a hard disc drive includes a pivot bearing cartridge, a pivot housing (arm or e-block), a record head gimbal assembly (HGA), an actuator voice coil, the flexible circuit for receiving and sending the electrical signal in and out to the recording head and the actuator, and additional components. The flexible circuit is connected to pivot housing by press-pin and soldering methods. The flexible circuit is re-routed in a ‘S’ loop shape by a re-routing tip feature on the pivot housing at one end and by a flexible circuit stiffener at the other end.
Flexible circuit resonance has been a common problem in disc drives for generations of products. When a hard disc drive is engaged in a data seeking process, the flexible circuit is moving together with the pivot housing at the connected end. The flexible circuit motion/vibration/resonance can be large enough to cause functional failure for the drive, e.g. the slider is unable to settle out above the commanded track as rapidly as required. (This is referred to as the seek settle out requirement). As each new generation of hard disc drive demands more recorded tracks per inch (KTPI), fixing or reducing the flex resonance becomes more important.
Known approaches for modifying the flex resonance generally fall into two types. The first approach is to change the geometry of the flexible circuit (longer or shorter length, thinner or thicker flex, etc) to change the natural resonant frequency of the flexible circuit. This type of fix needs to be re-addressed in the product development cycle for each new generation of hard disc drive as the natural frequency of the flexible circuit varies depending on the specific design of the flexible circuit, i.e., length, thickness, etc. The second approach is to add damping material on the moving part (loop area) of the flexible circuit to absorb the energy. This approach does not control or damp the flex resonance energy transfer at the contacting area between the flexible circuit and pivot housing. When the drive runs a short seek and needs to settle on a track, the flexible circuit may not be able to synchronize with the pivot housing to stop its motion in time. Instead, the inertia force keeps the flexible circuit moving and this extra inertia motion energy transfers directly to the pivot housing, causing the system to fail to meet seek settle out requirements. Consequently, neither approach is entirely satisfactory.
Embodiments of the present invention address these and other problems, and offer other advantages over the prior art.